fix: 添加单条记录GET端点，修复移动端编辑表单数据加载

- work-plans/mini-business/key-visits 均新增 GET /{id} 端点
- 三个移动端编辑表单改用单条端点加载数据
- 修复点击卡片进入编辑时空白的 bug

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/api/key_visits.py

@@ -49,6 +49,21 @@ async def list_key_visits(
     return [await _enrich(k, db) for k in result.scalars().all()]
 
 
+@router.get("/{item_id}")
+async def get_key_visit(
+    item_id: str,
+    current_user: dict = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    result = await db.execute(select(KeyVisit).where(KeyVisit.id == item_id))
+    k = result.scalar_one_or_none()
+    if not k:
+        raise HTTPException(status_code=404, detail="Not found")
+    if current_user["role"] == "manager" and str(k.manager_id) != current_user["user_id"]:
+        raise HTTPException(status_code=403, detail="Access denied")
+    return await _enrich(k, db)
+
+
 @router.post("/")
 async def create_key_visit(
     data: KeyVisitCreate,

backend/app/api/mini_business.py

@@ -48,6 +48,21 @@ async def list_mini_business(
     return [await _enrich(m, db) for m in result.scalars().all()]
 
 
+@router.get("/{item_id}")
+async def get_mini_business(
+    item_id: str,
+    current_user: dict = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    result = await db.execute(select(MiniBusiness).where(MiniBusiness.id == item_id))
+    m = result.scalar_one_or_none()
+    if not m:
+        raise HTTPException(status_code=404, detail="Not found")
+    if current_user["role"] == "manager" and str(m.manager_id) != current_user["user_id"]:
+        raise HTTPException(status_code=403, detail="Access denied")
+    return await _enrich(m, db)
+
+
 @router.post("/")
 async def create_mini_business(
     data: MiniBusinessCreate,

backend/app/api/work_plans.py

@@ -48,6 +48,21 @@ async def list_work_plans(
     return [await _enrich(w, db) for w in result.scalars().all()]
 
 
+@router.get("/{item_id}")
+async def get_work_plan(
+    item_id: str,
+    current_user: dict = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    result = await db.execute(select(WorkPlan).where(WorkPlan.id == item_id))
+    wp = result.scalar_one_or_none()
+    if not wp:
+        raise HTTPException(status_code=404, detail="Not found")
+    if current_user["role"] == "manager" and str(wp.manager_id) != current_user["user_id"]:
+        raise HTTPException(status_code=403, detail="Access denied")
+    return await _enrich(wp, db)
+
+
 @router.post("/")
 async def create_work_plan(
     data: WorkPlanCreate,